Method for growing superconductive film

Abstract: A method for growing a superconductive film, comprising: (a) helically winding a tape substrate around the outer periphery of a cylindrical or columnar holder and (b) growing a superconductive film on the surface of the tape substrate by plasma flash evaporation, while rotating the holder and a cylindrical or columnar holder for a tape substrate for growing a superconductive film. According to the present invention, the heat contact between the holder and the tape substrate is stabilized and a high performance tape conductor can be obtained. In addition, degradation of superconductive performance possibly experienced, when the tape is used for a transmission cable or the like, can be lessened. Furthermore, the large area growth, which is the characteristic feature of plasma flash evaporation, is effectively utilized and production efficiency of a long tape conductor can be enhanced.

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for growing a superconductive film and a holder of a tape substrate for growing a superconductive film. More particularly, the present invention relates to a method for growing a superconductive film using a holder of a tape substrate for growing a superconductive film thereon by plasma flash evaporation. BACKGROUND OF THE INVENTION A plasma flash evaporation is a method for growing a film having a desired composition, which includes introducing a powder of a starting material into an ultrahigh temperature plasma, thereby subjecting the powder to evaporation and condensation. The method is characterized by high speed growth and large area growth. The tape substrate and the substrate holder are heated by the thermal plasma and a system for heating the substrate holder is not necessary. Fig. 4 depicts a conventional method for growing a superconductive film by plasma flash evaporation. According to the conventional method, a tape substrate 12 is brought into contact with an upper surface 11a of a fixed plane holder 11, and the tape is run toward the direction of an arrow B in this contact state, while applying a thermal plasma P to grow a superconductive film on the tape substrate 12, whereby a tape conductor is obtained. In Jap. J. of Appl. Phys., 27 (6), June 1988, pages L1092 - L1093, a superconductive tape is prepared by atmospheric plasma spraying of superconductive material on heated tape substrates wound around a drum which is rotated during spraying. The tape requires post-annealing. In the conventional method, however, a large area growth, which is the characteristic feature of the plasma flash evaporation, is not advantageously utilized, since the superconductive film is grown only on a part of the plane holder 11. In addition, since the tape substrate 12 runs on the upper surface 11a of the fixed plane holder 11, the heat contact between the holder 11 and the tape substrate 12 is unstable, and a high performance tape conductor is difficult to obtain. A tape conductor having a superconductive film is mainly used for transmission cables and superconductive magnets. For applying the tape conductor for these uses, the tape conductor needs to be solenoidally wound. However, superconductors are known to markedly lose superconductive performance by tensile distortion and bending distortion. Therefore, the tape conductor produced by a conventional method is susceptible to degradation of superconductive performance, when it is wound solenoidally, due to the bending deformation developed in the superconductor. Under the circumstances, the present invention aims at providing a method of growing a superconductive tape using a holder of a tape substrate for growing a superconductive film, which permits effective utilization of the beneficial characteristics of the plasma flash evaporation; provides a high performance tape conductor by the stable heat contact between a tape substrate and the holder; and decreases degradation of superconductive performance potentially experienced when the tape conductor is used for a transmission cable. SUMMARY OF THE INVENTION The present invention relates to (1) a method of growing a superconductive tape, comprising: (a) helically winding a tape substrate around the outer periphery of a cylindrical or columnar holder and (b) growing a superconductive film on the surface of the tape substrate by plasma flash evaporation while rotating the holder; and (2) a cylindrical or columnar holder having a tape substrate helically wound around the outer periphery of the holder being used in the method of growing a superconductive film as defined in (1) above. Fig. 1 shows one embodiment of the method for growing a superconductive film of the present invention. Fig. 2 shows the results of an X-ray diffraction of the tape conductor obtained in Example 1. Fig. 3 shows superconductive transition temperature of the tape conductor obtained in Example 1. Fig. 4 shows a conventional method for growing a superconductive film by plasma flash evaporation. DETAILED DESCRIPTION OF THE INVENTION According to the substrate holder (the holder of a tape substrate for growing a superconductive film is hereinafter referred to as the substrate holder) used in the method according to the present invention, a tape substrate can be helically wound around the outer periphery of the holder, since the holder is columnar or cylindrical in shape, thus permitting effective utilization of the surface of the holder. Accordingly, the area exposed to the thermal plasma during plasma flash evaporation increases and the large area growth, which is the characteristic feature of plasma flash evaporation, can be effectively utilized, which in turn results in an improved production efficiency of a long tape conductor. According to the method for growing a superconductive film of the present invention, moreover, the heat contact between the holder and the tape substrate is stable, since the tape substrate is helically wound around the outer periphery of the substrate holder of the present invention, and a superconductive film is formed on the surface of the tape substrate by plasma flash evaporation while rotating the holder, whereby a high performance tape conductor can be obtained. In addition, since a superconductive film is grown on the surface of the tape substrate solenoidally wound, degradation of superconductive performance, possibly experienced when the tape is used for a transmission cable, can be lessened. Furthermore, the use of the substrate holder of the present invention results in effective utilization of the large area growth, which is the characteristic feature of plasma flash evaporation, and an enhanced production efficiency of a long tape conductor. Fig. 1 shows one embodiment of the method for growing a superconductive film of the present invention. In Fig. 1, a tape substrate 2 is helically wound around an outer periphery 1a of a columnar holder 1, which is one embodiment of the substrate holder of the present invention. The holder 1 is connected to a rotation drive means 4, such as a motor, via a rotation axis 3, and rotates toward the direction of an arrow A. A superconductive film is grown on the tape substrate 2 in a gas for growing a desired superconductive film, by heating with the thermal plasma P. In the present invention, the shape of the holder 1 may be columnar or cylindrical with a hollow part therein. While the diameter of the holder 1 varies depending on the use of the tape conductor having a superconductive film formed thereon it is generally 10 mm - 100 mm, preferably 20 mm - 50 mm, and the entire length of the holder 1 is 50 mm - 300 mm, preferably 70 mm - 150 mm. The material of the holder 1 is a heat resistant metal, such as stainless steel and Hastelloy, or a ceramic such as alumina. As the tape substrate 2, usable are platinum, alumina polycrystals, yttria-stabilized zirconia (YSZ) polycrystals, calcia-stabilized zirconia (CSZ) polycrystals and heat resistant metals covered with these. While the width of the tape substrate 2 varies depending on the use of the tape conductor, it is generally 2 mm - 20 mm, preferably 5 mm - 10 mm. For forming a superconductive film on the surface of the tape substrate 2, argon, oxygen and a starting material such as a superconductive oxide powder are introduced into a reaction chamber. Examples of the superconductive oxide powder include YBa 2 Cu 3 Ox, Bi 2 Sr 2 CaCu 2 Ox and (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 Ox. A mixture of predetermined amounts of CuO, Y 2 O 3 , BaCO 3 , Bi 2 O 3 , SrCO 3 CaCO 3 and PbO may be also used. Then, the holder 1 is applied with a high frequency electricity of 2 MHz - 13.56 MHz, while rotating the holder 1 at 0.1 rpm - 10 rpm under a gas pressure of 66.7 - 667 mbar (1mbar = 100 Pa) (50 - 500 Torr). When a long tape conductor usable for superconductive wire or current lead is manufactured, a means for delivering a tape substrate 2 and a means for winding up same may be set in the vicinity of the holder 1. The tape conductor thus obtained can reduce degradation of superconductive performance, which may occur when the tape conductor is used for transmission cable. Even when the tape may be used in a linear state such as for a current lead, the degradation of superconductive performance is less, since the tape conductor is subject to compression distortion. The present invention is described in more detail in the following by an illustrative Example and Experimental Example, Example 1 A 10 mm wide YSZ polycrystal tape was helically wound around the outer periphery of a 25 mm diameter columnar holder, and a powder of YBa 2 Cu 3 O x was supplied under an environment of 226 mbar (200 Torr) and argon gas/oxygen gas of 7/50 (volume ratio) to form a film at 600°C holder temperature for 10 minutes. After forming the film, the holder was naturally cooled and the specimen was taken out when it became 100°C or below. Experimental Example 1 The X-ray diffraction and superconductive transition temperature of the obtained tape conductor were determined, the results of which are shown in Fig. 2 and Fig. 3, respectively. The results of the X-ray diffraction as shown in Fig. 2 reveal the diffraction peak of the YSZ polycrystal and the peak of superconductor phase. Based on the resistance values shown in Fig. 3, it is known that the superconductive transition temperature is near 90 K. Using the substrate holder the large area growth, which is the characteristic feature of plasma flash evaporation, can be effectively utilized and production efficiency of a long tape conductor can be enhanced. According to the method for growing a superconductive film of the present invention, moreover, the heat contact between the holder and the tape substrate is stabilized and a high performance tape conductor can be obtained. In addition, degradation of superconductive performance, possibly experienced when the tape is used for a transmission cable can be lessened. Furthermore, the large area growth, which is the characteristic feature of plasma flash evaporation, is effectively utilized and production efficiency of a long tape conductor can be enhanced.

Claims: A method of growing a superconductive tape, comprising: (a) helically winding a tape substrate around the outer periphery of a cylindrical or columnar holder and (b) growing a superconductive film on the surface of the tape substrate by plasma flash evaporation while rotating the holder. A cylindrical or columnar holder having a tape substrate helically wound around the outer periphery of the holder, said holder being used in the method of growing a superconductive film according to claim 1.

Inventors: SHIOHARA YOH, TATSUMI NORIYUKI, TSUJINO JIRO, YUHYA SHIGENORI, SHIOHARA, YOH, TATSUMI, NORIYUKI, TSUJINO, JIRO, YUHYA, SHIGENORI, SHIOHARA, YOH, C/O SUPERCON. RES. LAB., TATSUMI, NORIYUKI, C/O SUPERCON. RES. LAB., TSUJINO, JIRO, C/O SUPERCON. RES. LAB., YUHYA, SHIGENORI, C/O MITSUBISHI CABLE IND. LTD.
Applicants: HOKKAIDO ELECTRIC POWER, INT SUPERCONDUCTIVITY TECH, MITSUBISHI CABLE IND LTD, INTERNATIONAL SUPERCONDUCTIVITY TECHNOLOGY CENTER, MITSUBISHI CABLE INDUSTRIES, LTD., THE HOKKAIDO ELECTRIC POWER COMPANY INC.
Application year: 1994
Main classification: H01L39
IPC codes: C23C14, C30B29, H01L39, C01G3, C01G1